The present invention relates to a device for protecting a container containing a pressurized fluid. Such a device can in particular be used for protecting against overpressures a circuit or receptacle functioning under pressurized water or steam.
The invention is advantageously used in protecting the main primary circuits of pressurized water nuclear reactors. The device according to the invention can in particular be connected to the upper dome of the pressurizer associated with the primary circuit of such a reactor. However, it should be noted that the present device can be used for protecting other types of container.
At present, protection of the main primary circuit of a pressurized water nuclear reactor against overpressures involves the use of a certain number of elements, particularly discharge valves and safety valves with respect to the pressurizer, which have an essential function. More specifically, three spring-operated safety valves are used, each of them being connected to the upper dome of the pressurizer by a non-thermally insulated swan neck-shaped pipe, which makes it possible for a water plug to form upstream of the valves due to condensation. These valves are calibrated to 172 bars. In parallel, three discharge valves, which open on an all or nothing basis, with assisted pneumatic motorization and closing through shortage of air are connected to the upper dome of the pressurizer by pipes, whose arrangement also makes it possible to form a water plug by condensation. Two of these valves are calibrated at 162 bars, the third being controlled by a proportional integral derived control system. Upstream individual isolation of each discharge valve is provided by a motorized electrical valve, whose essential function is to permit the isolation of a discharge valve, which would lose its sealing effect.
Although the existing protection device is satisfactory on an overall basis, it still has certain disadvantages associated more particularly with the following problems:
the presently used safety valves operate unstably under certain conditions, there is a risk of a drift in the calibration points, and a risk of sealing loss, which makes it necessary to carry out highly disadvantageous checks and maintenance;
the existence of a water plug upstream of the safety valves leads to risks of flapping or swinging during the passage of said water plug and as a result said valve can be blocked in a more or less open position and if this situation is taken into account in safety analyses, it can lead to very serious consequences with regards to the operating material and the availability of the section;
the control of isolating valves and discharge valves is relatively complex through the need of ensuring the automatic closing of the isolating valves below a certain threshold, with the aim of limiting the consequences of depressurization by an untimely opening or non-closing of the discharge valves;
the isolating valves must be carefully checked after each operation under full flow, which represents a very unsatisfactory operating constraint;
the risk of failure on closing of safety valves has consequences, which may be considered acceptable from the safety standpoint, but which are sufficiently serious from the operating standpoint and the availability of the section, for the possibility of the isolation of these valves to be seriously considered.
In view of these various problems, it is desirable to have anovel device able to fulfil the same functions as the prior art devices, which can rapidly and automatically isolate a primary gap or break caused by an unsatisfactory reclosing of a safety valve and considerably reduce maintenance constraints with respect to the protective equipment of the primary circuit.
However, it is clear that even if the protective device according to the invention is particularly suitable for protecting the primary circuit of a pressurized water reactor, it can also be used in the protection of other than nuclear containers, particularly when it is desirable to automatically isolate a valve for increasing availability and reducing maintenance and work on important members and not for safety reasons.